REFLEX AND CONDITIONED ACTION 51 



the final stage in this process. The absence of specifi- 

 city or of physiological domination by any one sen- 

 sori-motor behavior pattern is their most character- 

 istic feature. Otherwise they would be incapable of 

 performing the marvelous feats of recombination and 

 redintegration of sensory experience which come to 

 expression in intelligently directed behavior and in 

 creative imagination. 



We conclude that during the progress of verte- 

 brate evolution the complexity of stereotyped be- 

 havior patterns has increased and parallel with this 

 the structure of the brain stem has been compli- 

 cated by the fabrication of numerous specific reflex 

 centers, all interrelated by well-insulated fiber tracts. 

 This is the apparatus of routine behavior — immediate 

 sensori-motor reactions. Now, if these numerous 

 stabilized components of behavior are on occasion 

 to be combined in unaccustomed ways or redirected 

 to new ends — if, in short, the animal so generously 

 endowed with reflexes and instincts is able to learn 

 to do new things — then the switchboards into which 

 all these processes are converged must be corre- 

 spondingly enlarged. 



The thalamus and the cerebral cortex are such 

 centers where many diverse systems of accustomed 

 nervous activities may impinge and react one upon 

 another. These parts of the brain retain even in the 

 highest animals something of that generalized or non- 

 specific sort of nervous organization which is so 



